Cushman, et al. in U.S. Pat. No. 4,052,511 discloses angiotensin converting enzyme inhibitors of the formula ##STR4## wherein
R.sub.1 and R.sub.4 each is hydrogen, lower alkyl or phenyl lower alkyl;
R.sub.2 is hydroxy, amino, hydroxyamino or lower alkoxy;
and n is 0 to 2.
Ondetti, et al. in U.S. Pat. No. 4,154,935 discloses hyportensive agents of the formula ##STR5## wherein
R is hydrogen, lower alkanoyl or ##STR6##
R.sub.3 and R.sub.4 is each hydrogen, lower alkyl or trifluoromethyl; and n is 0 or 1.
Ondetti, et al. in U.S. Pat. No. 4,105,776 disclose angiotensin converting enzyme inhibitors of the formula ##STR7## wherein
R.sub.1 is hydrogen or lower alkyl;
R.sub.2 is hydrogen, R.sub.5 --CO--, R.sub.6 --S-- or R.sub.7 ;
R.sub.5 is lower alkyl;
R.sub.6 is lower alkyl;
n is 0, 1 or 2;
and R.sub.7 is ##STR8##